A copending patent application by James S. Congdon, Ser. No. 61,158, filed July 26, 1979, U.S. Pat. No. 4,276,516, shows an integrated circuit (IC) power transistor structure designed to improve heat dissipation. The IC layout is disclosed in relation to the overall chip topography. Another copending patent application by James S. Congdon, Ser. No. 56,489, filed July 11, 1979, U.S. Pat. No. 4,263,563, shows a distortion reduction circuit for a power amplifier. This invention relates to such amplifiers and is directed to a circuit for limiting their maximum temperature.
In a typical Class AB or Class B amplifier, the output stage dissipation rises with signal level. In many cases, this can result in excessive temperatures that can damage the output devices. Such excessive dissipation can result from load faults or merely from sustained high signal conditions. In order to avoid damaged output devices, it is common to sense the device temperature and when some maximum is exceeded to either shut the devices off, or to reduce their operating current or voltage.
The invention is directed to a circuit useful in that type of temperature control in which the heat generating devices are shut down, when their temperature rises above some predetermined level.